The present invention relates to a feed unit for strip wrapping material.
The invention is exploitable advantageously for the purpose of applying an adhesive substance to a strip of sheet material as used by machines for the manufacture of tobacco products, the art field to which reference is made explicitly in the following specification albeit with no limitation in general scope implied.
More precisely, the present invention relates to a roller type gumming device utilized in a filter tip attachment to apply a layer of adhesive to a continuous strip of paper, which is then divided into discrete lengths, or single tipping papers, serving ultimately to join together filters and relative cigarette sticks.
The prior art embraces the solution of applying an adhesive to a continuous strip of paper material by means of a gumming device consisting in a pair of rollers contrarotating about horizontal axes and engaging one with another resiliently along an area of mutual contact. One such roller functions as a transfer roller and the other as the gumming roller proper, its surface revolving tangentially to the continuous strip of paper material.
The transfer roller and gumming roller combine to establish a trough between the two mutually opposed portions of their respective revolving cylindrical surfaces converging immediately above the area of mutual contact aforementioned, whilst the space directly above the trough is occupied by the nozzle of a pipeline connected to a tank filled with the adhesive.
The trough extends along the entire straight line generator of contact between the rollers and holds a reserve of the adhesive from which to prime the gumming roller.
The direction of rotation of the gumming roller is such that the layer of adhesive can be applied by the outer cylindrical surface of the selfsame roller to the continuous strip of material at a point downstream of the area along which contact is made with the transfer roller. The thickness of the layer of adhesive is controlled by the pressure of the contact between the two rollers.
It has been found that adhesives of the type in question need to be maintained at a predetermined and substantially constant temperature throughout the gumming process. Should the temperature happen to stray outside well defined limits, in effect, the adhesive will lose its physical and chemical properties such as viscosity, bonding power, etc., and can then no longer be spread uniformly over the strip material.
The object of the present invention is to provide a gumming device unaffected by the aforementioned drawback.